Wideband Code Division Multiple Access (WCDMA) telecommunication systems have many attractive properties that can be used for future development of telecommunication services. A specific technical challenge in e.g. WCDMA and similar systems is the scheduling of enhanced uplink channels to time intervals where the interference conditions are favourable, and where there exist a sufficient capacity in the uplink of the cell in question to support enhanced uplink channels. It is well known that existing users of the cell all contribute to the interference level in the uplink of WCDMA systems. This is because all users and common channels of a cell transmit in the same frequency band when CDMA technology is used. The load of the cell is directly related to the interference level of the same cell.
In order to retain stability of a cell, the load needs to be kept below a certain level. This follows since the majority of uplink user channels, at least in WCDMA, are subject to power control. This power control aims at keeping the received power level of each channel at a certain signal to interference ratio (SIR), in order to be able to meet specific service requirements. This SIR level is normally such that the received powers in the Radio Base Station (RBS) are several dBs below the interference level. Despreading in so-called RAKE-receivers then enhances each channel to a signal level where the transmitted bits can be further processed, e.g. by channel decoders and speech codecs later in the signal processing chain.
Since the RBS tries to keep each channel at its specific preferred SIR value, it may happen that an additional user raises the interference level, thereby momentarily reducing the SIR for the other users. The response of the RBS is to command a power increase to all other users, something that increases the interference even more. Normally this process remains stable below a certain load level. In case a high capacity channel would suddenly appear, the raise in the interference becomes large and the risk for instability, a so called power rush, increases. It is thus a necessity to schedule high capacity uplink channels, like the E-UL channel in WCDMA, so that one can insure that instability is avoided. In order to do so, the momentary load must be estimated in the RBS. This enables the assessment of the capacity margin that is left to the instability point.
The load of a cell in a CDMA system is usually expressed as the noise rise, or the rise over thermal (ROT). The exact mathematical definitions will be defined in detail in the description below. Here it is sufficient to state that in order to establish a noise rise estimate the noise floor (ideally thermal noise) and the total power level need to be known. The total power level is easily measured in the receiver. The noise floor is however more difficult to assess. Estimates of the noise floor according to prior art is typically associated with relatively large uncertainties, which even may be in the same order of magnitude as the entire available capacity margin. It will thus be very difficult indeed to implement enhanced uplink channels functionality without improving load estimations connected thereto.